High molecular weight polyacrylamide synthesis

ABSTRACT

This invention discloses a process for the polymerization of acrylamide and for the copolymerization of acrylamide with other monomers. It employs a ferrous/hydroperoxide redox initiator system that greatly enhances the molecular weight of the polymer formed. These high molecular weight acrylamide polymers offer outstanding advantages in enhanced oil recovery as injection water viscosifiers.

This application is a continuation-in-part of Ser. No. 649,622, filed onSept. 12, 1984, now abandoned.

BACKGROUND OF THE INVENTION

After using conventional pumping techniques very large amounts of oil ina given reservoir remain unrecovered. In an attempt to recover this vastquantity of unpumped petroleum many enhanced oil recovery (EOR)techniques have been developed. The water flooding method is a verycommon EOR technique that has been in use for some time. Water floodingis a secondary oil recovery technique that is chiefly of importance whenthe natural production of a well has ceased--that is, when petroleum canno longer be pumped from the well economically using conventionalpumping techniques. The term "secondary recovery" as used herein, refersto all petroleum recovery operations used in such areas when spontaneousproduction of the well can no longer be effected. It includes what issometimes known in the industry as "tertiary recovery," which is a laterstage which begins when the petroleum reservoir is substantially"flooded out" and a large amount of water may be produced before any oilis recovered. Thus, primary recovery is when a well spontaneously flowsusing conventional pumping techniques and secondary recovery begins whenprimary recovery is no longer feasible and continues for as long asthere is any petroleum in the well which can be economically or feasiblyremoved.

The water flooding technique comprises injecting water into a petroleumdeposit through at least one input well (injection well), therebycausing the petroleum to flow from that area for collection through atleast one output well. In the simplest recovery method a number of wellsare drilled on the circumference of a circle and a final well is drilledin the center. Water is then pumped into one or more of the wells,typically the ones on the circumference, under high pressure and forcedthrough the petroleum-bearing formations, usually porous rock strata.The petroleum remaining in the strata is forced out by the oncomingwater and removed through the output well, usually the one at the centerof the circle. More typically an array of injection and production(output) wells are established over an oil field in a manner that willoptimize this secondary recovery technique by taking into account thegeological aspects of that particular field. Ideally, the water shoulddisplace 100 percent of the petroleum in the oil field.

Even though water may pass through a deposit, the inherentincompatibility of oil and water, variation in reservoir rock, includingpermeability variation, faults and shale barriers may result in someregions of the reservoir rock being by-passed so that large oil bearingareas in the deposit remain untouched. This results in less than 100percent of the residual oil in the reservoir being recovered. Theability of water, or any other fluid, to displace oil is related to thatfluid's mobility ratio. Every fluid has a specific mobility in an oildeposit, which can be defined as the ease with which that fluid flowsthrough a porous medium divided by the viscosity of that fluid. Amobility ratio is the ratio of the mobility of two fluids: for example,oil and water. If a fluid flows much more easily than oil through areservoir, it will readily bypass oil deposits within the reservoirrather than pushing them toward producing wells. Thus, fluids with lowmobility ratios are greatly preferred for enhanced oil recoveryapplications. Recovery by water flooding techniques is greatlyfacilitated if the mobility of the petroleum relative to the injectionwater is at a maximum. This is frequently accomplished by increasing theviscosity of the aqueous medium and decreasing the viscosity of thepetroleum, by the addition of suitable chemical agents. Thus, athickener is ordinarily added to the water while a thinning agent may becharged into the petroleum.

High molecular weight (above about 1,000,000) water soluble polymers aregenerally added to the injection water used in EOR applications toimprove the mobility ratio of the water to the oil. A very largeincrease in water viscosity can be obtained when certain polymers areadded in minor amounts (100 ppm to 1500 ppm). Two general types ofpolymers are currently being used as injection water viscosifiers., theyare polyacrylamides and polysaccharides. In general, partiallyhydrolyzed and anionic polyacrylamides are used, but cationicpolyacrylamides have also been used in a limited number of cases. Themobility ratio improvement obtained using polyacrylamides decreases withwater salinity and divalent ion concentration. Therefore, a fresh watersource (total dissolved solids less than 10,000 ppm) has traditionallybeen necessary for the effective use of polyacrylamides in EORapplications as viscosifiers. The environment into which thepolyacrylamide solution is injected has traditionally also been requiredto be substantially free of salts in order to be effective.

SUMMARY OF THE INVENTION

This invention reveals a process for the synthesis of ultra-highmolecular weight polyacrylamide. This ultra-high molecular weightpolyacrylamide has excellent properties as an injection waterviscosifier for EOR applications. Even though polyacrylamide synthesizedby utilizing the process of this invention is sensitive to metal saltsits viscosity in aqueous solutions is sufficient to allow for its use insalty environments (in the presence of brine). Such ultra-high molecularweight polyacrylamide is also of great value in environments that aresubstantially free of salts since its ability to viscosify water perunit weight is greater than polyacrylamide of lesser molecular weight.

The process of this invention is also applicable in copolymerizations ofacrylamide with other vinyl monomers. For example, in some cases it isdesirable to copolymerize acrylamide with a metal salt of2-acrylamido-2-methyl propane sulfonic acid (AMPS) in order to make thepolymer being synthesized more resistant to hydrolysis (decomposition byreaction with water).

This invention reveals a process for the homopolymerization ofacrylamide and for the copolymerization of acrylamide with vinylmonomers comprising initiating said homopolymerization or saidcopolymerization with a ferrous/hydroperoxide redox initiator system andcarrying out said homopolymerization or said copolymerization in anaqueous reaction medium at a temperature of from about -20° C. to about40° C.

This invention also discloses a process for the homopolymerization ofacrylamide and for the copolymerization of acrylamide with vinylmonomers; comprising: initiating said homopolymerization or saidcopolymerization with a ferrous/hydroperoxide redox system and carryingout said homopolymerization or said copolymerization in an aqueousreaction medium in the presence of a molecular weight jumper of thestructural formula: ##STR1## wherein M represents a member selected fromthe group consisting of Na, K, and NH₄ ; and wherein Z and Z' can be thesame or different and represent a member selected from the groupconsisting of Na, K, NH₄, alkyl groups containing from 10 to 40 carbonatoms, aryl groups containing from 10 to 40 carbon atoms, alkyl-ethergroups containing from 10 to 40 carbon atoms, and aryl-ether groupscontaining from 10 to 40 carbon atoms.

DETAILED DESCRIPTION

Ultra-high molecular weight polyacrylamide and acrylamide copolymers canbe synthesized in an aqueous medium or in a water-in-oil dispersionutilizing the process of the invention. Polyacrylamide has thestructural formula: ##STR2## wherein n is an integer. Acrylamidecopolymers are polymers that contain at least about 40 percent by weightacrylamide repeat units (repeat units which are derived fromacrylamide). The remaining repeat units in acrylamide copolymers arevinyl monomer repeat units (repeat units which are derived from vinylmonomers other than acrylamide). These repeat units differ from thevinyl momomers that they were derived from in that their vinylcarbon-carbon double bond has been consumed in the polymerization. Forexample, if N,N-dimethylacrylamide is copolymerized with acrylamide theN,N-dimethylacrylamide repeat units will have the structural formula:##STR3## and the resulting acrlyamide/N,N-dimethylacrylamide copolymerproduced will have the structural formula: ##STR4## wherein n and m areintegers and wherein indicates that the distribution of repeat unitsderived from acrylamide and N,N-dimethylacrylamide can be random.

The vinyl monomers that can be employed in copolymerizations withacrylamide must contain at least one vinyl group (CH₂ ═CH--). Thesevinyl monomers generally contain from 2 to 16 carbon atoms. Such vinylmonomers can also contain nitrogen, oxygen, halogens, sodium, calcium,and potassium. The maximum amount of a vinyl monomer that can becopolymerized with acrylamide to produce a useful polymer will varygreatly. A person skilled in the art will be able to ascertain thisamount through routine experimentation. Generally, such acrylamidecopolymers will contain no more than about 50 percent by weight vinylmonomer repeat units. In some cases the amount of vinyl monomer repeatunits that it is desirable to incorporate into the polymer will be lessthan 5 percent by weight, based upon the total repeat units in thepolymer. In many cases vinyl monomers can be polymerized into acrylamidecopolymers without necessarily improving or adversely affecting theproperties of the polymer produced. Alpha-olefins and lightlyhalogenated α-olefins containing from 2 to 16 carbon atoms are examplesof such vinyl monomers that do not greatly affect the properties of thepolymer produced when they are copolymerized with acrylamide in smallquantities. Since aliphatic vinyl monomers have a low solubility inwater it generally will not be possible to polymerize large quantitiesof such monomers into the acrylamide copolymers of this invention byemploying an aqueous polymerization system without utilizing soaps.

Vinyl monomers with the structural formula: ##STR5## wherein R, R', R"can be the same or different and represent a hydrogen atom, a methylgroup, or an ethyl group; wherein X represents --NH-- or --0--; whereinA represents an alkylene group containing from 1 to 4 carbon atoms;wherein M represents Na, K, Ca, or NH₄ ; and wherein n is 1 or 2, arethe preferred vinyl monomers for the copolymerizations of thisinvention. If M is Na, K, or NH₄, then n will be 1 and if M is Ca, thenn will be 2. Repeat units derived from vinyl monomers of this type tendto make the copolymer produced more resistant to hydrolysis. It isgenerally preferred for R to be an hydrogen atom or a methyl group. Thealkylene group (represented as A) can be a straight chain or branched.

A representative example of a straight chain alkylene group is shown inthe following structural formula:

    --CH.sub.2 --CH.sub.2 --CH.sub.2 --

A representative example of a branched chain alkylene group is shown inthe following structural formula: ##STR6##

The most preferred vinyl monomers for copolymerization into acrylamidecopolymers are metal and ammonium salts of 2-acrylamido-2-methylpropanesulfonic acid (AMPS). Copolymers of this type have a very high viscosityin fresh water, maintain excellent viscosities in saline solutions andare resistant to hydrolysis. Sodium AMPS (sodium2-acrylamido-2-methylpropanesulfonate), potassium AMPS (potassium2-acrylamido-2-methylpropanesulfonate), ammonium AMPS (ammonium2-acrylamido-2-methylpropanesulfonate) and calcium AMPS (calcium2-acrylamido-2-methylpropanesulfonate) are all useful as monomers in thesynthesis of ultra-high molecular weight acrylamide copolymers. ##STR7##

The aqueous polymerizations of this invention are carried out in anaqueous reaction medium comprising: water, monomers and aferrous/hydroperoxide redox initiator system. It is generally preferredfor the aqueous reaction medium to also contain a molecular weightjumper.

Ultra-high molecular weight polyacrylamide and acrylamide copolymers canbe synthesized in an aqueous medium over a very wide temperature rangefrom about -20° C. to about 40° C. The monomer charge concentration usedin an aqueous solution synthesis of polyacrylamide and acrylamidecopolymers can be varied over a wide range from as low as about 2 weightpercent to as high as about 60 weight percent of the total reactionmedium (monomers, water, initiators, molecular weight jumper, etc.).Generally, it is preferred to use a monomer charge concentration (totalconcentration of all monomers in the aqueous reaction medium) in therange of 15 to 55 weight percent. For example, 80 parts of water, 19parts of acrylamide and 1 part of sodium AMPS (20 weight percent monomercharge concentration) can be employed in the polymerization recipeutilized in the synthesis of ultra-high molecular weight copolymers ofacrylamide and sodium AMPS.

The amount of metal or ammonium AMPS useful in such copolymerizationscan range from as low as 0.01 weight percent to as high as 50 weightpercent of the total monomer charge. In such copolymerizations generallyfrom 5 weight percent to 20 weight percent of a metal or ammonium AMPSwill be employed based upon the total monomer charge if a copolymerwhich is resistant to hydrolysis is desired.

The ultra-high molecular weights that are attained by practicing theprocess of this invention are achieved through the use of aferrous/hydroperoxide redox initiator system. This initiator system hasbeen unexpectedly found to yield molecular weights which are much higherthan those achieved when typical redox initiator systems are utilized.For instance, weight average molecular weights of greater than40,000,000 can easily be attained. Molecular weight jumpers can be usedin conjunction with the ferrous/hydroperoxide redox initiator system ofthis invention to attain even higher molecular weights. For example,molecular weight jumpers can be used to attain polymers with weightaverage molecular weights of greater than 60,000,000. These molecularweight jumpers must be present in the reaction medium during the courseof the polymerization.

Numerous ferrous/hydroperoxide redox initiator systems can be used toinitiate the polymerizations of this invention. However, the redoxsystems used will be water soluble and thus soluble in the aqueousreaction medium. These ferrous/hydroperoxide redox initiator systems arecomprised of a ferrous compound which contains a divalent iron atom(Fe²⁺) and a hydroperoxide compound which contains a --OOH group. Forexample, ferrous sulfate heptahydrate, FeSO₄.7H₂ O, has been used inconjunction with paramenthane hydroperoxide as a redox initiation systemin the polymerizations of this invention with great success. Somerepresentative examples of ferrous compounds that can be used in theredox initiator systems of this invention include ferrous ammoniumgluconate, ferrous bromide, ferrous carbonate, ferrous chloride, ferrousfluoride, ferrous fluosilicate, ferrous hyposulfite, ferrous iodide,ferrous nitrate, ferrous oxalate, ferrous nitrate, ferrous sulfate,ferrous tartrate, and ferrous thiocyanate. Some representative examplesof hydroperoxide compounds that can be utilized include

2,3-dimethylbutane hydroperoxide,

methylcyclohexane hydroperoxide,

p-cumene hydroperoxide,

2,2,5-trimethylhexane hydroperoxide,

1,2,3,4-tetrahydronaphthalene hydroperoxide,

sec-butylbenzene hydroperoxide,

p-cymene hydroperoxide, p0 aliphatic alkylate hydroperoxide,

1-methyl-1,2,3,4-tetrahydronaphthalene hydroperoxide

5-phenylpentene-2-hydroperoxide,

chloroisopropylbenzene hydroperoxide,

cyclohexylbenzene hydroperoxide,

diisopropylbenzene hydroperoxide,

isopropyl-1,3,3,4-tetrahydronaphthalene hydroperoxide,

t-butylisopropylbenzene hydroperoxide,

diisopropyltoluene hydroperoxide,

1,2,3,4,4a,9,20,10a-octahydrophenanthrene hydroperoxide,

5-(4-iospropylphenyl-2-pentene hydroperoxide,

(1-methylbutyl)-isopropylbenzene hydroperoxide,

chlorodiisopropylbenzene hydroperoxide,

triisopropylbenzene hydroperoxide,

1,2-diphenylbutane hydroperoxide,

di-t-butylisopropylbenzene hydroperoxide,

(1-methylhendecyl)-toluene hydroperoxide,

1,2-bis-(dimethylphenyl)-butane hydroperoxide, and

(1-methylhendecyl)-isopropylbenzene hydroperoxide.

The most preferred hydroperoxide compounds are 2,3-dimethylbutanehydroperoxide, cumene hydroperoxide sec-butylbenzene hydroperoxide,p-cymene hydroperoxide, and paramenthane hydroperoxide. The ferrouscompound can be employed at levels from about 0.000001 weight percent to0.05 weight percent based upon the total weight of the aqueous reactionmedium. It is generally preferred for this component to be employed atlevels from about 0.000003 weight percent to about 0.005 weight percentbased upon the total weight of the aqueous reaction medium. The mostpreferred level for the ferrous component is from 0.000005 to 0.00001weight percent based upon the total weight of the aqueous reactionmedium. Optimal results are generally obtained at a concentration of theferrous compound of about 0.000007 weight percent based upon the totalweight of the aqueous reaction medium in homopolymerizations ofacrylamide and in copolymerizations containing large amounts ofacrylamide in comparison to other monomers. The hydroperoxide compoundcan be employed at levels from about 0.0001 to 0.05 weight percent basedupon the total weight of the aqueous reaction medium. It is generallypreferred for the hydroperoxide to be employed at a level of 0.0005 to0.02 weight percent with a level of 0.001 to 0.01 weight percent beingmost preferred.

The temperature range over which the polymerization of this inventioncan be conducted is from about -20° C. to about 40° C. The preferredtemperature range is from -5° C. to 20° C. with the most preferredtemperature being from -2° C. to 5° C. The reaction time (time periodbetween the initiation of the polymerization and its termination) isgenerally in the range of about 0.5 to 18 hours. However, in most casesa reaction time of 1.5 to 3 hours can be employed. This reaction timewill vary with the temperature at which the polymerization is conductedwith the type of redox initiator system employed and with the level ofinitiator used.

It is sometimes desirable to use deionized water in the preparation ofthe aqueous reaction medium used in the polymerizations of thisinvention. For best results oxygen which is dissolved in the water andmonomers should be removed before polymerization. This can beaccomplished by sparging the monomers and water used in the reactionmedium with an inert gas or nitrogen.

The molecular weight jumpers that are useful in the practice of thisinvention have the structural formula: ##STR8## wherein M represents amember selected from the group consisting of Na, K, and NH₄ and whereinZ and Z' can be the same or different and represent a member selectedfrom the group consisting of Na, K, NH₄, alkyl groups containing from 10to 40 carbon atoms, aryl groups containing from 10 to 40 carbon atoms,alkyl-ether groups containing from 10 to 40 carbon atoms, and aryl-ethergroups containing from 10 to 40 carbon atoms. In most cases wherein Z isNa, K, or NH₄ ; Z' will be an alkyl group, an aryl group, an alkyl-ethergroup or an aryl-ether group. In the converse situation wherein Z' isNa, K, or NH₄ normally Z will be an alkyl group, an aryl group, analkyl-ether group or an aryl-ether group. These molecular weight jumpersare generally prepared by reacting maleic anhydride with an appropriatealcohol containing at least 10 carbon atoms followed by the addition ofa metal bisulfite, such as sodium bisulfite. A general description ofthis synthesis technique is given in U.S. Pat. Nos. 2,028,091 and2,176,423 which are incorporated herein by references in their entirety.

Alkyl-ether groups are aliphatic hydrocarbon radicals that contain oneor more "oxy" linkages (--0--). Some representative examples ofalkyl-ether groups include: ##STR9## Aryl-ether groups are aromatichydrocarbon radicals that contain one or more "oxy" linkages (--0--).The term alkyl group as used herein includes what is sometimes referredto as a cycloalkyl group. In other words the term alkyl group as usedherein includes all aliphatic hydrocarbon radicals including those withstraight chain branched chain, and cyclic (ring) structures. The arylgroups normally employed contain an aliphatic component and aresometimes referred to as aralkyl groups.

The preferred molecular weight jumpers for use in this invention arethose wherein Z and Z' are selected from the group consisting of Na; K:NH₄ ; alkyl groups containing from 12 to 30 carbon atoms; alkyl-ethergroups of the structural formula: ##STR10## wherein T and T' can be thesame or different and represent a hydrogen atom, a methyl group, or anethyl group, wherein a and b are integers, wherein indicates that thedistribution of repeat units can be in any order, and wherein thealkyl-ether group contains from 12 to 30 carbon atoms; aryl-ether groupsof the structural formula: ##STR11## wherein T and T' can be the same ordifferent and represent a hydrogen atom, a methyl group, or an ethylgroup, wherein a, b, and c are integers, wherein indicates that thedistribution of repeat units can be in any order, wherein chain linkagesthrough the benzene ring can be in an ortho, meta, or para orientation,and wherein the aryl-ether group contains from 12 to 30 carbon atoms.

In the most preferred molecular weight jumpers for use in this inventionZ' is Na or K and Z is an alkyl group containing from 12 to 15 carbonatoms or an aryl-ether group with the structural formula: ##STR12##wherein d is an integer from 1 to 6, wherein e is an integer from 2 to10, and wherein f is an integer from 1 to 20, and wherein the sum of d,e, and f (d +e +f) is from 12 to 24. Some representative examples ofmolecular weight jumpers that are most preferred for use in thisinvention include: Aerosol™ A-102 (sold by American Cyanamid) which hasthe structural formula: ##STR13## wherein x is 4 or 5 and wherein y is10 to 12; and bis-n-tridecyl sodium sulfosuccinate which has thestructural formula: ##STR14##

The polymerizations of this invention can be carried out in an aqueousreaction medium to obtain ultra-high molecular weight polyacrylamide andacrylamide copolymers. These polymerizations can be initiated by theaddition of a redox system to a mixture of water, the monomers, and themolecular weight jumper which forms an aqueous reaction medium. It isnot necessary for the molecular weight jumper to be present at the timethat the polymerization is first initiated (it can be added later), butit is generally desirable for the molecular weight jumper to the presentfrom the start of the polymerization.

The amount of molecular weight jumper that can be employed in theaqueous reaction media of this invention will generally range from about2 weight percent to about 20 weight percent based on the total weight ofthe reaction medium. Lesser amounts of molecular weight jumper can beused, but by employing less than 2 percent by weight of the molecularjumper in a reaction medium only minimal increases in the molecularweight of the polyacrylamide or acrylamide copolymer being synthesizedwill result. On the other hand, greater amounts ( 20 weight percent) ofmolecular weight jumper can also be employed, but such use of additionalmolecular weight jumper generally does not result in molecular weightsthat are greater than those observed when more moderate amounts ofmolecular weight jumper is used. In other words, a molecular weightmaximum is reached and the use of additional amounts of molecular weightjumper will not result in significant increases in molecular weightabove this maximum. The molecular weight maximum is generally reached ata molecular weight jumper level in the reaction media of 8 to 12 phm(parts per 100 parts of monomer by weight).

The preferred amount of molecular weight jumper for use in the aqueousreaction media of this invention ranges from 4 weight percent to 15weight percent. The most preferred amount of molecular weight jumper foruse in the reaction media of this invention ranges from 10 weightpercent to 12 weight percent based upon the total weight of the reactionmedia.

These aqueous polymerizations which yield ultra-high molecular weightpolyacrylamide and acrylamide copolymers result in the formation of awater soluble gel-like mass. This water soluble polymer must bedissolved in additional water in order to be utilized as a viscosifierfor EOR applications. These polymers should be dissolved in anappropriate amount of water to provide a polymer concentration that willresult in the desired viscosity for the injection water. Obviously theviscosity of the injection water increases with increasing polymerconcentrations. Generally it will be desirable to have an injectionwater viscosity (Brookfield) of about 2 to about 30 cP (centipoise) forEOR applications.

When preparing these solutions care should be taken so as to preventshear forces from causing molecular fracture in the polymer chains ofthese polymers. In order to prevent molecular fracture when dissolvingthese polymers in water vigorously mixing, shaking, etc. shouldgenerally be avoided. The occurrence of such molecular fracture inducedby shearing forces can significantly reduce the molecular weight of thepolymer and therefore its usefulness as an EOR viscosifier (viscositieswould be reduced). In order to dissolve these polymers in water theymust be allowed to dissolve over a very long period of time. Ultra-highmolecular weight acrylamide copolymers and ultra-high molecular weightpolyacrylamide are very valuable as EOR injection water viscosifierssince their ultra-high molecular weight allows them to viscosify anaqueous solution to a given viscosity at lower polymer concentrationsthan do corresponding acrylamide polymers of lesser molecular weight.The ability of an EOR polymer to viscosify water increases withincreasing molecular weight; therefore, the ferrous/hydroperoxide redoxinitiator system of this invention is very valuable because it can beused to increase the molecular weight of polyacrylamide and acrylamidecopolymers.

The polyacrylamide and acrylamide copolymers of this invention can alsobe synthesized in an aqueous reaction medium utilizing water-in-oildispersion polymerization techniques. The ultra-high molecular weightpolymers produced in an aqueous reaction media by water-in-oildispersion polymerization techniques are in the form of a liquid (incontrast to the gel-like mass formed in standard aqueouspolymerizations). This liquid can easily be further diluted to thedesired polymer concentration for use as injection water for EORapplications. This further dilution can be achieved almost immediatelyupon mixing with additional water. The ultimate properties of theacrylamide copolymers and polyacrylamide produced by water-in-oildispersion polymerizations are equivalent to the properties of theircounterparts produced by standard aqueous polymerization (they have thesame excellent properties as EOR viscosifiers). Water-in-oil dispersionpolymerization offers a very substantial advantage over standard aqueouspolymerization in that the ultra-high molecular weight polymers producedcan be easily and rapidly dissolved (further diluted) in the injectionwater.

The water-in-oil dispersion synthesis of polyacrylamide and acrylamidecopolymers is run utilizing the same monomer charge composition, redoxinitiators, and reaction conditions as is used in the standard aqueouspolymerization synthesis of these ultra-high molecular weight polymers.In water-in-oil dispersion polymerization in addition to the reagentsused in standard aqueous polymerizations, there is also present an oiland normally a dispersing agent. Some representative examples of oilsthat can be used are kerosene, diesel fuel, pentane, hexane, decane,pentadecane, benzene, toluene, 2,4-dimethylhexane, mineral oil (liquidpetrolatum), and 3-ethyloctane. This is certainly not an exhaustive listof the oils that can be employed. Most alkanes containing 5 or morecarbon atoms will work very well as will most aromatic hydrocarbons.Alkenes should not be used since they can react in the polymerization.The dispersing agents are nonionic surfactants that are soluble inhydrocarbons and insoluble in water. Some representative examples ofdispersing agents that may be used in water-in-oil dispersionpolymerization include polyethers, such as Igepal CO-430™ (GAF Corp.);polyglycerol oleates, such as Witconol-14™ (Witco Chemical Company); andpolyglycerol stearates, such as Witconol-18L™ (Witco Chemical Company).##STR15## These dispersing agents (nonionic surfactants) are added tothe oil that will be used in the water-in-oil dispersion polymerization.Normally, the oil used in such dispersion polymerizations will containfrom about 2 to about 10 weight percent of the dispersing agent.Normally, the aqueous reaction medium used in these water-in-oildispersion polymerizations will contain 25 weight percent of the oilcontaining the dispersing agent based on the total aqueous reactionmedium. Even more oil can be used in such water-in-oil dispersionpolymerization with a corresponding increase in the amount of dispersingagent used but generally it will not be advantageous to use largeramounts of the oil. Good results can be obtained using an aqueousreaction medium comprising about 25 weight percent monomers, about 50weight percent water, and about 25 weight percent oil. A chargecomposition containing less than 25 weight percent monomers can be used,however, it will not normally be advantageous to use lesser quantitiesof the monomers.

It is often desirable to use deionized water in such water-in-oildispersion polymerizations. Oxygen which is dissolved in the monomers,water, and oil should be removed before polymerization. This can beaccomplished by sparging the monomers, water, and oil with an inert gasor nitrogen. Such a mixture of monomers, water, and oil is vigorouslymixed to obtain the water-in-oil dispersion. The dispersion is broughtto the desired temperature (normally about 0° C.) and the initiatorcomponents are added. The aqueous reaction medium containing the redoxinitiators system is normally stirred or in some alternative wayagitated during the course of the polymerization.

After the desired reaction time the polymerization can be terminated byadding a shortstopping agent, such as methylether hydroquinone; however,this will normally not be necessary. Normally, this reaction time willbe from about 1.5 to about 3 hours. The desired reaction time will varywith reaction temperature, initiator concentration, and the degree ofpolymerization desired. Normally, it will be desirable to allow thepolymerization to go to completion (until the monomer supply isessentially exhausted).

In the polymerizations of this invention yields are essentiallyquantitative (in excess of 99 percent). The percentage of repeat unitsby weight derived from a monomer in a polymer will be equal to thepercentage by weight of that monomer in the aqueous reaction medium usedin the synthesis of that polymer.

The present invention will be described in more detail in the followingexamples. These examples are merely for the purpose of illustration andare not to be regarded as limiting the scope of the invention or themanner in which it may be practiced. Unless specifically indicatedotherwise, all parts and percentages are given by weight.

EXAMPLE 1

A vial was charged with a 50 percent aqueous acrylamide solution. Thisacrylamide monomer solution was degassed by a continuous nitrogensparge. Polymerization was initiated by injecting aferrous/hydroperoxide redox initiator system into the vial. Thisferrous/hydroperoxide system contained ferrous sulfate heptahydrate(FeSO₄.7H₂ O) and paramethane hydroperoxide. In this example 0.000007%ferrous sulfate heptahydrate and 0.0055% paramenthane hydroperoxide,based upon the total weight of the aqueous reaction medium, was added tothe vial. Polymerization was conducted with the vial being immersed inan ice water bath for a period of about 12 hours. This polymerizationresulted in the production of a polymer cement.

An aqueous brine solution having a polymer concentration of 2500 ppm(parts per million) was prepared by placing the proper amount of polymercement from the vial in 400 ml (milliliters) of brine water and waitingfor complete dissolution which took several days. One-hundred percentmonomer conversion was assumed in the preparation of this solution. Thebrine water solution employed in this example contained 3 percent NaCland 0.3 percent CaCl₂. The Brookfield viscosity of the polymer-brinesolution was determined to be 22.4 cP (centipoise). Brookfieldviscosities are perhaps of greater importance in the characterization ofan EOR polymer than is molecular weight. In any case, increases inBrookfield viscosities are indicative of increases in the molecularweight of the polymer in the solution being tested and it was determinedby comparing the Brookfield viscosity of the solution made with thepolymer synthesized in this experiment with the Brookfield viscositiesof solutions made with polymers of known molecular weights that thepolymer synthesized in this experiment had a weight average molecularweight of about 70,000.000. The very high Brookfield viscosity of thesolution made in this experiment indicated that a very excellent EORpolymer was made utilizing the process of this invention.

EXAMPLE 2

This experiment was done as a comparative example using the sameprocedure as was specified in Example 1 except that a typical redoxinitiator system was employed instead of the ferrous/hydroperoxidesystem used in Example 1. The redox initiator system utilized in thisexperiment contained 0.002% sodium meta-bisulfite (Na₂ S₂ O₅) and 0.002%ammonium persulfate, based upon the total weight of the aqueous reactionmedium. The Brookfield viscosity of the solution made in this experimentwas only 4.5 cP. Thus, this example clearly shows that theferrous/hydroperoxide redox initiator system of this invention producessuperior EOR polymers to those produced using standard redox systems.

EXAMPLE 3

This example is included in order to show that molecular weight jumperscan be used to further increase the molecular weight of polyacrylamidesmade using a ferrous/hydroperoxide redox initiator system. Thisexperiment was done using the same procedure as was specified in Example1 except that the polymerization was conducted in the presence of 5% ofAerosol™ A-102, based upon the total weight of the aqueous reactionmedium. The Brookfield viscosity of the solution made in this experimentwas determined to be 27.2 cP with its weight average molecular weightbeing determined to be about 80,000,000. Thus, the presence of themolecular weight jumper Aerosol™ A-102 substantially improved themolecular weight of the polymer produced.

EXAMPLE 4

This experiment was done using the same procedure as was specified inExample 1 except that the redox initiator system utilized contained0.0025% by weight (NH₄)₂ S₂ O₈ and 0.0015% by weight FeSO₄.7H₂ O. TheBrookfield viscosity of the solution made in this experiment was only1.7 cP. This experiment shows that ferrous/hydroperoxide redox initiatorsystems are far superior to the standard redox system tested in thisexperiment for use in synthesizing EOR polymers.

EXAMPLE 5

This experiment was done as a comparative example using the sameprocedure as was specified in Example 1 except that a conventional redoxinitiator system was utilized. The redox initiator system employed inthis experiment contained 0.2 weight percent tetraethylene pentamine and0.006 weight percent p-menthane hydroperoxide. The Brookfield viscosityof the solution made in this experiment was only 7.5 cP. This experimentagain shows the superiority of ferrous/hydroperoxide redox initiatorsystems for use in producing EOR polymers.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the scope of the invention.

What is claimed is:
 1. A process for the homopolymerization ofacrylamide and for the copolymerization of acrylamide with vinylmonomers to produce ultra-high molecular weight water soluble polymerscomprising initiating said homopolymerization or said copolymerizationwith a ferrous/hydroperoxide redox initiator system and carrying outsaid homopolymerization or said copolymerization in an aqueous reactionmedium at a temperature of from about -20° C. to about 40° C.; whereinthe ultra-high molecular weight polymer produced has a weight averagemolecular weight of greater than about 40,000,000.
 2. A process asspecified in claim 1 wherein said ferrous/hydroperoxide redox initiatorsystem is comprised of a ferrous compound selected from the groupconsisting of ferrous ammonium gluconate, ferrous bromide, ferrouscarbonate, ferrous fluoride, ferrous fluosilicate, ferrous hyposulfite,ferrous iodide, ferrous nitrate, ferrous oxalate, ferrous nitrate,ferrous sulfate, ferrous tartrate and ferrous thiocyanate which is usedin conjunction with a hydroperoxide compound selected from the groupconsisting of 2,3-dimethylbutane hydroperoxide, ferrous nitrate, ferroussulfate, ferrous tartrate, and ferrous thiocyanate which is used inconjunction with a hydroperoxide compound selected from the groupconsisting of2,3-dimethylbutane hydroperoxide, methylcyclohexanehydroperoxide, cumene hydroperoxide, 2,2,5-trimethylhexanehydroperoxide, 1,2,3,4-tetrahydronaphthalene hydroperoxide,sec-butylbenzene hydroperoxide, p-cymene hydroperoxide, aliphaticalkylate hydroperoxide, 1-methyl-1,2,3,4-tetrahydronaphthalenehydroperoxide, 5-phenylpentene-2-hydroperoxide, chloroiospropylbenzenehydroperoxide, cyclohexylbenzene hydroperoxide, diisopropylbenzenehydroperoxide, isopropyl-1,3,3,4-tetrahydronaphthalene hydroperoxide,t-butylisopropylbenzene hydroperoxide, diisopropyltoluene hydroperoxide,1,2,3,4,4a,9,20,10a-octahydrophenanthrene hydroperoxide,5-(4-iospropylphenyl-2-pentene hydroperoxide,(1-methylbutyl)-isopropylbenzene hydroperoxide, chlorodiisopropylbenzenehydroperoxide, triisopropylbenzene hydroperoxide, 1,2-diphenylbutanehydroperoxide, di-t-butylisopropylbenzene hydroperoxide,(1-methylhendecyl)-toluene hydroperoxide,1,2-bis-(dimethylphenyl)-butane hydroperoxide, and(1-methylhendecyl)-isopropylbenzene hydroperoxide.
 3. A process asspecified in claim 2 wherein said ferrous compound is present in saidaqueous reaction medium at levels from about 0.000001 weight percent toabout 0.05 weight percent and wherein said hydroperoxide compound ispresent in said aqueous reaction medium at levels from about 0.0001 toabout 0.05 weight percent based upon the total weight of the aqueousreaction medium.
 4. A process as specified in claim 3 wherein from about2 weight percent to about 60 weight percent monomers are present in theaqueous reaction medium based upon the total weight of the aqueousreaction medium.
 5. A process as specified in claim 4 wherein saidtemperature is from about -5° C. to 20° C.
 6. A process as specified inclaim 5 wherein said ferrous compound is present in said aqueousreaction medium at levels from about 0.000003 weight percent to 0.005weight percent based upon the total weight of the aqueous reactionmedium and wherein said hydroperoxide is present in said aqueousreaction medium at levels from about 0.0005 weight percent to 0.02weight percent based upon the total weight of the aqueous reactionmedium.
 7. A process as specified in claim 6 wherein from about 15weight percent to about 55 weight percent monomers are present in theaqueous reaction medium based upon the total weight of the aqueousreaction medium.
 8. A process as specified in claim 7 wherein said vinylmonomers have the structural formula: ##STR16## wherein R, R', and R"can be the same or different and represent a hydrogen atom, a methylgroup, or an ethyl group; wherein X represents --NH-- or --0--; whereinA represents an alkylene group containing from 1 to 4 carbon atoms;wherein M represents Na, K, Ca, or NH₄ with the proviso that if M is Na,K, or NH₄, then n will be 1 and if M is Ca, then n will be
 2. 9. Aprocess as specified in claim 8 wherein said ferrous compound is ferroussulfate and wherein said hydroperoxide compound is paramethanehydroperoxide.
 10. A process as specified in claim 9 wherein saidaqueous reaction medium further comprises a molecular weight jumper ofthe structural formula: ##STR17## wherein M represents a member selectedfrom the group consisting of Na, K, and NH₄ and wherein Z and Z' can bethe same or different and represent a member selected from the groupconsisting of Na, K, NH₄, alkyl groups containing from 10 to 40 carbonatoms, aryl groups containing from 10 to 40 carbon atoms, alkyl-ethergroups containing from 10 to 40 carbon atoms, and aryl-ether groupscontaining from 10 to 40 carbon atoms.
 11. A process as specified inclaim 10 wherein Z and Z' are selected from the group consisting of Na;K; NH₄ alkyl groups containing from 12 to 30 carbon atoms; alkyl-ethergroups of the structural formula: ##STR18## wherein T and T' can be thesame or different and represent a hydrogen atom, a methyl group, or anethyl group, wherein a and b are integers, wherein indicates that thedistribution of repeat units can be in any order, and wherein thealkyl-ether group contains from 12 to 30 carbon atoms; aryl-ether groupsof the structural formula: ##STR19## wherein T and T' can be the same ordifferent and represent a hydrogen atom, a methyl group, or an ethylgroup, wherein a, b, and c are integers, wherein indicates that thedistribution of repeat units can be in any order, wherein chain linkagesthrough the benzene ring can be in an ortho, meta, or para orientation,and wherein the aryl-ether group contains from 12 to 30 carbon atoms.12. A process as specified in claim 1 wherein Z' is selected from thegroup consisting of Na and K, and wherein Z is an alkyl group containingfrom 12 to 15 carbon atoms or an aryl-ether group with the structuralformula: ##STR20## wherein d is an integer from 1 to 6, wherein e is aninteger from 2 to 10, and wherein f is an integer from 1 to 20, andwherein the sum of d, e, and f (d+e+f) is from 12 to
 24. 13. A processas specified in claim 10 wherein Z and Z' are alkyl groups containingfrom 12 to 30 carbon atoms.
 14. A process as specified in claim 10wherein Z and Z' are alkyl groups containing from 12 to 15 carbon atoms.15. A process as specified in claim 10 wherein said molecular weightjumper has the structural formula ##STR21## wherein x is 4 or 5 andwherein y is 10 to
 12. 16. A process as specified in claim 10 whereinsaid molecular weight jumper has the structural formula ##STR22##wherein n is 8 or
 9. 17. A process as specified in claim 10 wherein saidmolecular weight jumper is bis-n-tridecyl sodium sulfosuccinate.
 18. Aprocess as specified in claim 11 wherein said vinyl monomers areselected from the group consisting of sodium2-acrylamido-2-methylpropanesulfonate, potassium2-acrylamido-2-methylpropanesulfonate, ammonium2-acrylamido-2-methylpropanesulfonate and (calcium2-acrylamido-2-methylpropanesulfonate).
 19. A process for thehomopolymerization of acrylamide and for the copolymerization ofacrylamide with vinyl monomers to produce ultra-high molecular weightwater soluble homo- or copolymers comprising: initiating saidhomopolymerization or said copolymerization with a ferrous/hydroperoxideredox system and carrying out said homopolymerization or saidcopolymerization in an aqueous reaction medium in the presence of amolecular weight jumper of the structural formula: ##STR23## wherein Mrepresents a member selected from the group consisting of Na, K, and NH₄and wherein Z and Z' can be the same or different and represent a memberselected from the group consisting of Na, K, NH₄, alkyl groupscontaining from 10 to 40 carbon atoms, aryl groups containing from 10 to40 carbon atoms, alkyl-ether groups containing from 10 to 40 carbonatoms, and aryl-ether groups containing from 10 to 40 carbon atoms;wherein the ultra-high molecular weight polymer produced has a weightaverage molecular weight of greater than about 60,000,000.
 20. A processas specified in claim 19 wherein said ferrous/hydroperoxide redoxinitiator system is comprised of ferrous sulfate which is used inconjunction with paramethane hydroperoxide; wherein said aqueousreaction medium is at a temperature of from about -20° C. to about 40°C.; wherein said ferrous sulfate and said paramenthane hydroperoxide arepresent in said aqueous reaction medium at levels of from about 0.0005weight percent to 0.01 weight percent based upon the total weight of theaqueous reaction medium; wherein from about 2 weight percent to about 60weight percent monomers are present in the aqueous reaction medium basedupon the total weight of the aqueous reaction medium; and wherein saidvinyl monomers have the structural formula: ##STR24## wherein R, R', R"can be the same or different and represent a hydrogen atom, a methylgroup, or an ethyl group; wherein X represents --NH-- or --0--; whereinA represents an alkylene group containing from 1 to 4 carbon atoms;wherein M represents Na, K, Ca, or NH₄ with the proviso that if M is Na,K, or NH₄, then n will be 1 and if M is Ca, then n will be 2.